Fatal error: Uncaught Error: Interface "Drupal\webform\Plugin\WebformElementInterface" not found in /home/www/drupal8/test/modules/webform/src/Plugin/WebformElementEntityReferenceInterface.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/Plugin/WebformElementEntityReferenceInterface.php on line 10